The Spence Shale was named by Walcott (1880) as a member of the Ute Formation and described as argillaceous shales, and he later added the words of sandy shales.
It was named in honor of Robert S. Spence of Garden City, Utah, who in 1896 and subsequent years sent some interesting and well-preserved fossils to Dr. Charles D. Walcott at the U.S. National Museum. His doing so led to Dr. Walcott's studies and collections at Spence's discovery site and other localities in southern Idaho and northern Utah.
Williams and Maxey (1941) later recognized that the Spence Shale was a member of the Langston Formation, separated from the Brigham Quartzite by only a few feet of crystaline limestone.
More recent authors have used the name Spence to refer to the Spence Tongue of the Lead Bell Shale, the preferred usage today.

The lower part of the Spence, containing agnostid trilobites, consists of dark silty micrite and gray to gray black laminated shales considered to represent outer detrital-belt environments. The upper part of the Spence lacks agnostids and has some thin-bedded limestone.
Below the Spence Shale is the Naomi Peak Limestone, which represents the middle carbonate bank, and the massive Brigham Quartzite below it represents the inner detrital belt.
Spence Shale of variable thickness crops out at several localities in the Wasatch Mountains north of Brigham City and in its eastern spur, the Bear River Range, extending into southern Idaho.

At left are showed the typical gray shales of the Spence Shale member

Large, heterogenous order with primitive origins and problematic classification, with specialized offshoots that are hard to frame within a general diagnosis.

Cephalon typically with opisthoparian facial sutures, with gently forward-tapering simple glabella bearing a broad, rounded front, usually with 3 pairs of rather narrow parallel glabellar furrows; natant hypostome. Thorax typically large with 8+ thoracic segments. Pygidium quite variable, but typically with a small pygidium bearing a border (Cambrian) or a larger pygidium with or without border (post-Cambrian).
From: http://www.trilobites.info/ordptychopariida.htm

Amecephalus idahoense, Resser, 1939

Ord.: PTYCHOPARIIDA
Fam.: ALOKISTOCARIDAE
Gen.: Amecephalus, WALCOTT, 1924b

Border of cranidium wide and flat except for low boss in front of glabella and shallow border furrow; glabella defined by strong axial furrow, eyes ridge crossing fixigenae and librigenae spined. Thorax with about 19 segments; pygidium small.

Amecephalus laticaudum, Resser, 1939

Ord.: PTYCHOPARIIDA
Fam.: ALOKISTOCARIDAE
Gen.: Amecephalus, WALCOTT, 1924b

Border of cranidium very wide and flat except for low boss in front of glabella and shallow border furrow; glabella defined by strong axial furrow, eyes ridge crossing fixigenae and librigenae well developed. Thorax with about 19 segments; pygidium small (see the upper right image).

Chancia ebdome, Walcott, 1924

Ord.: PTYCHOPARIIDA
Fam.: ALOKISTOCARIDAE
Gen.: Chancia, WALCOTT, 1924

Frontal area shorter and less bowed forward that in Alokistocare, glabella defined by axial furrows, eye ridges crossing fixigenae, librigenae spined; thorax with 19 to 22 segments, pleurae with well defined furrows. pygidium small.

Spencia typicalis, Resser, 1939a

Ord.: PTYCHOPARIIDA
Fam.: PTYCHOPARIIDAE
Gen.: Spencia, RESSER, 1939a

Strongly convex, anteriorly rounded glabella with lateral furrows; eye ridges distinct; palpebral lobes short, librigenae with poorly developed genal spines. Thorax with rounded extremities and little pygidium.

A specimen of Gogia sp. is visible on the right side of the picture.

Syspacephalus spencei (?), Resser, 1939a

Ord.: PTYCHOPARIIDA
Fam.: PTYCHOPERIIDAE
Gen.: Syspacephalus, RESSER, 1936

Glabella low, sloping down anteriorly; anterior border furrow more or less obsolete medially; palpebral lobes anterior to glabellar mid-point; anterior facial sutures convergent; genal angle rounded. Thorax of 13 to 15 segments. Exoskeleton slightly flattened. Pygidium small.

Cephalon with opisthoparian sutures; glabella elongate, sides often concave (pestle-shaped), furrows (when not effaced) typically with splayed arrangement, the hind pair pointing sharply backwards, and anterior pairs tending more and more forward directed; sometimes furrows pit-like; cranidial borders often ledgelike; hypostome conterminant or (in derived forms) impendent; eyes typically large, in some gently arcuate.
Thorax typically with 7-8 segments (but range for order is 2-12, rarely more), pleural tips often spinose.
Pygidium typically large (isopygous or subisopygous), of variable form, sometimes spinose. 
From: http://www.trilobites.info/ordcorynexochida.htm

Athabaskia bithus, Walcott, 1916

Ord.: CORYNEXOCHIDA
Fam.: DOLICHOMETOPIDAE
Gen.: Athabaskia, RAYMOND, 1928

Border of cranidium very wide and flat except for low boss in front of glabella and shallow border furrow; glabella defined by strong axial furrow, eyes ridge crossing fixigenae and librigenae well developed. Thorax with about 19 segments; pygidium small (see the upper right image).

Zacanthoides idahoensis, Walcott, 1908

Ord.: CORYNEXOCHIDA
Fam.: ZACANTHOIDIDAE
Gen.: Zacanthoides, WALCOTT, 1888

Glabella parallel-sided; metafixigenal spides present. Long semicircular palpebral lobesThorax of 9 segments; pleurae obliquely furrowed; no macropleural segments. Axial macro-spine on last axial segment. Pygidium smaller than cephalon with elevated,  abruptly terminated axis; general outline subtriangular; pleural fields flat; marginal furrow and border indistinct; pleurae directed backward, extended intoseveral pairs of marginal spines

Glossopleura bion, Walcott, 1916

Ord.: CORYNEXOCHIDA
Fam.: DOLICHOMETOPIDAE
Gen.: Glossopleura, POULSEN, 1927

Long palpebral lobe, slightly tapering posterior area of fixigenae. Cranidium without anterior border; axial furrows effaced between anterior corners of glabella; genal angles produced into into fairly strong, backward-directed genal spines. Thorax with 7 segments, wide axis and pointed extremities. Pygidium sligthly smaller than cephalon with indistinctly segmented pleural fields and well defined wide, concave border. Spines are presents in this specimen starting from 5th, 6th and 7th axial segments.

Phylum: Echinodermata
Class: Crinoidea
Order: Crinozoa
Family: Eocrinoidea
Genus: Gogia

Species: Gogia spiralis ? (probably new species)

GIS, Remote Sensing, Geologia, Geomorfologia, 3D, DEM, Mining, Trilobiti, Stromatoliti, Lagerstätten
Contacts: Enrico Bonino

Questo sito è affiliato al Club Paleontologico Italiano

Powered by WebRing.